I always try to speed up the disintergration of the steel wool by wetting it with as much vinegar it will hold while in an old pie tin (aluminum). Then put it out in the sun to dry. Use heavy rubber gloves, like the Playtex type or so, and scrunch up the dry rusty ball over the pie tin to save all of the rust dust. The gloves keep the tiny shards of steel wool from making like cactus spines and sticking into your fingers.
Put all of the rust dust into the vinegar. It does settle to a black sludge on the bottom of the bottle. This just speeds up the vinegars acid breaking down the steel wool. Shake the daylights out of it before pouring into a tray to treat the wood. I usually make sure the wood is well submerged and lightly shlosh the solution back and forth over the wood when first submerged to get any air bubbles off of it and get some of the sludge to settle out on the wood. Usually soak it for a min of 20 minutes. I've had excellent results even with angle stock or wide pieces of scribed stock. Just make sure you get all parts of the wood wet right away to avoid warps. Rule of thumb: a single ball of 0000 or 000000 steel wool in a half gallon of white vinegar will result in a solution that will generally give you a lighter gray, slightly brownish red wood. The more rust dust in the vinegar, say three or four balls per half gallon will push the wood color to oxide red. The "heavier" the solution, the more oxide red you will get. I have also just dropped the balls of steel wool into the jar of vinegar if I didn't need it right away, it will dissolve.
Regardless of the strength of the solution, you can force different colors. Drying in the sun will result in a yellowish, light gray. I dry my wood in the oven. Drying at about 175 to 200 degrees until dry, will result in a light brown/gray for week solutions to a light boxcarish (that a word?) red. Using higher temps will drive the colors darker. The better results I've gotten is to use a fairly medium solution, say two balls worth of rust dust per half gallon, and dry at around 250 - 275 degrees. You generally get a fairly uniform medium gray, not the silver gray of Weather-it. Keeping it at the 275 for another 10 to 15 minutes after the wood is actually dry gives me darker grays with fades of dark brown and blacks in the wood. With the stronger solutions you get a darker oxide red. I lay out the wood on a sheet of heavy duty aluminum foil in any random order. At the higher temps the wood will often have much darker spots where the foil is raised over the oven rack bars and the wood touches there. Should your pieces be short enough to lay them in the "valleys" between the rack bars you'll be less likely to have the dark spots. If the oven is not all that clean, lay a sheet of foil over the wood because the vinegar vapors will do a fair job on loosening the light greases which will drip down on the wood. Do not go over 300 degrees because some of the smaller stuff, HO 2 x 4 or 2 x 6, will generally burn right after it gets dry. Especially as you open the oven door. And I mean heavy white smoke, a rosy orange flame and raucous smoke detector.
Lately I have kept the oven at 175 degrees for more control varying the time.